This invention relates to a surveillance system and method for aircraft approach and landing and, more particularly, a system and method that is well-suited for use on parallel runways under instrument meteorological conditions.
Various surveillance systems and methods have developed over the course of military and civilian aviation in the United States. Each new system and method generally builds on the existing technology and is compatible with the existing technology.
In the 1980s, the Federal Aviation Administration (FAA) recognized that parallel approaches to runways spaced less than 4,300 feet apart are restricted under instrument meteorological conditions (IMC) because of limitations in the current radars and displays. The limitations required air traffic controllers to use dependently sequenced approaches, so that if an aircraft blunders toward the adjacent approach, it would pass through a gap and not into another aircraft. Accordingly, the FAA instituted several initiatives to study various technologies to reduce the restrictions on parallel approaches and to develop a system and method that would improve the capacity of airports with parallel runways. Some of the results of the initiatives are summarized in R. LaFrey""s xe2x80x9cParallel Runway Monitor,xe2x80x9d 2 The Lincoln Laboratory Journal (Fall 1989), pp. 411-36, which is hereby incorporated by reference.
It was clear from the studies that the Parallel Runway Monitor (PRM), which the system and method to improve the capacity of airports with parallel runways was dubbed, required an increase in the surveillance update rate. The FAA developed two ways to increase the surveillance update rate. One was to put two Mode S antennas, facing in opposite directions, on the same rotating structure. The two-antenna approach resulted in a satisfactory update rate. The other approach was to use a circular array of many radiating elements, which could be individually excited in phase and amplitude to create a fan beam that could be pointed in any direction very quickly. The azimuth measurement in the circular array approach is a form of a monopulse. The update rate could be as high as desired, and in practice was set at once per second. The FAA selected the circular array method for monitoring closely spaced parallel approaches.
As more parallel runways are planned and small airports become more popular, there is incentive to reassess the PRM. Some elements of the PRM, such as the circular array antenna and its control system, are complicated and expensive. Other elements of the PRM, such as the processor, may not take full advantage of current computer processing capabilities. Airports may want to maximize the use of parallel runways that are more closely spaced than the PRM was designed to handle, and may therefore need an alternative to the PRM.
An objective of the present invention to provide information to an air traffic control system that will enable safe, independent aircraft arrivals at closely spaced parallel runways under instrument meteorological conditions. Another objective of the present invention is to provide such information without requiring modification to existing aircraft transponders.
In general, in one aspect, the invention is directed to a system for measuring and predicting information on the position of approaching aircraft. The system features a processor, an interrogating antenna, a receiving antenna, and a data link. The processor schedules interrogations and suppression pulses. Both of the antennas and the data link are in signal communication with the processor. The interrogating antenna transmits interrogations to a plurality of approaching aircraft. At least some of the interrogations include suppression pulses. The receiving antenna comprises at least three fixed, broad azimuth, array elements. The receiving antenna receives replies from each of the plurality of approaching aircraft and communicates the replies to the processor. The processor determines a state for each of the plurality of approaching aircraft based on the replies. The data link communicates information on the state of each of the plurality of approaching aircraft from the processor.
In another aspect, the invention is directed to a method of measuring and predicting information on the position of approaching aircraft. The method includes receiving surveillance data on a plurality of aircraft within a first volume, and filtering the data to identify a target list of aircraft. The target list of aircraft is determined by location within a volume at least partially defined by characteristics of a receiving antenna comprising at least three fixed, broad azimuth, array elements. The method also includes scheduling interrogations for the target list of aircraft, and storing the schedule of interrogations. The method further includes transmitting interrogations, at least some of the interrogations including suppression pulses, and receiving replies to the interrogations from each aircraft on the target list of aircraft. Finally, the method includes determining the state of each aircraft on the target list of aircraft based on the replies and the schedule of interrogations.
In another aspect, the invention is directed to a system for collecting and calculating information on the position of a plurality of approaching aircraft. The system features a memory buffer, a processor, and an output device. The memory buffer stores surveillance data on a plurality of aircraft within a first volume. The processor, which is in signal communication with the memory buffer and the output device, runs a plurality of modules. The modules include a filtering module, a scheduling module, and a tracking module. The filtering module identifies a target list of aircraft within a zone of interest from the surveillance data. The zone of interest is at least partially defined by characteristics of a receiving antenna comprising at least three fixed, broad azimuth, array elements. The scheduling module schedules interrogations based on the target list. At least some of the interrogations include suppression pulses. The tracking module calculates state information based on replies to interrogations from each of the plurality of aircraft on the target list. The output device communicates state information for each of the plurality of aircraft on the target list.
Embodiments of the foregoing aspects of the invention include the following features. The plurality of approaching aircraft, which may be on the target list, may be identified from surveillance data on the plurality of aircraft within a first volume from a nearby secondary radar, from flight plan information, from S-Mode squitters, from Mode S and Mode A/C interrogations, or from a combination of the foregoing. A suppression antenna may transmit P2 suppression pulses to the plurality of approaching aircraft. Replies may include transmissions from the plurality of approaching aircraft sent in response to the interrogations, Mode-S squitters, or both.
In some embodiments, calculating state information for each of the plurality of aircraft on the target list may include determining the azimuth of each aircraft based on the replies and the schedule of interrogations. Ambiguity in determining the azimuth of an aircraft on the target list of aircraft may be resolved using surveillance data from the nearby secondary radar. One or more pulses within a reply sent in response to an interrogation may suffice, in some embodiments, to determine the state of the responding aircraft; receiving the entirety of a standard reply to an interrogation may not be necessary to determine the state of the responding aircraft.
In some embodiments, the schedule of interrogations may be modified in response to a failure to receive a reply. For example, an interrogation including suppression pulses may be re-scheduled and re-transmitted if no reply to the original interrogation is detected. Interrogation characteristics, in some embodiments, may be modified based on the characteristics of replies received in response to one or more previous interrogations.
The foregoing and other aspects, features, and advantages of the invention will be apparent from the following description.